It is known to effect media conferencing by using a conference bridge. A conference bridge is a device that facilitates conferencing between multiple conference participants operating respective terminal units. In a typical interaction, the conference bridge receives a plurality of media signals from multiple conference participants and selects the participants that are determined to have the most active speech signal for transmission to the other participants of the conference.
In a packet-based communication system, the media signals are in the form of packets. The packets generally include encoded media information and header information. Typically, in such systems, the conference bridge receives the media data packets, decodes the encoded media information, and performs the selection of the most active speakers using the decoded media information on the basis of well-known methods. Following this, the conference bridge forms a mixed, composite media signal consisting of those selected media signals. The bridge forms a plurality of mixed, composite media signals, such that the signal of a given participant is either subtracted, or highly attenuated, from the composite media signal that is returned to him. The bridge then encodes the plurality media signals and forwards them to the appropriate participant of the conference. The terminal units at the participants' locations receive and decode the encoded media information and process the media information for delivery to the participants. U.S. Pat. No. 4,499,731 describes in greater detail the generating of mixed and composite media signals. The content of this document is hereby incorporated by reference.
A deficiency in systems of the type described above is, in the case where the encoding is a compression-type encoding, the degradation in the quality of the media information as the media information is encoded and decoded multiple times during the propagation of the media data packets. Another deficiency is that the encoding and decoding operations at the conference bridge require significant computing capabilities. Conference bridges and associated systems have been designed to reduce the occurrence of back-to-back (tandem) encode-decode operations. For further information regarding such conference bridges and such systems, the reader is invited to refer to the following co-pending patent applications:                U.S. patent application Ser. No. 09/475,047 entitled “Apparatus and Method for Packet-Based Media Communications” filed on Dec. 30, 1999 and assigned to the assignee of the present application;        U.S. patent application Ser. No. 09/750,015 entitled “Apparatus and Method for Packet-Based Media Communications” filed on Dec. 29, 2000 and assigned to the assignee of the present application;        U.S. patent application Ser. No. 09/664,450 entitled “Apparatus and Method for Packet-Based Media Communications” filed on Sep. 18, 2000 and assigned to the assignee of the present application.The contents of the above documents are herein incorporated by reference. The reader is also invited to refer to the following documents:        Forgie, J. W. and Feehrer, C. E. and Weene, P. L., “Voice Conferencing Technology Final Report”, MIT Lincoln Lab, March 1979, No. DDC ADA074498, Lexington, Mass.        Forgie, James W., “Voice conferencing in packet networks”, IEEE-ICC, pp. 21.3.1–21.3.4, June 1980, Seattle, Wash.        Champion, Terrence G., “Multi-speaker conferencing over narrowband channels”, IEEE-MILCOM, pp. 1220–1223, November 1991, Washington, D.C.        U.S. Pat. Nos. 5,457,685; 5,383,184; 5,317,567; 5,272,698; all entitled “Multi speaker conferencing over narrowband channels” and issued to Champion, Terrence G.        U.S. Pat. No. 5,390,177, issued to Nahumi, Dror entitled “Conferencing arrangement for compressed information signals”.        U.S. Pat. No. 5,436,896, issued to Anderson, Thomas W. et al., entitled “Conference bridge for packetized speech-signal networks”.        U.S. Pat. No. 5,570,363, issued to Holm, Robert E., entitled “Transform based scalable audio compression algorithms and low cost audio multi-point conferencing systems”.The contents of the above documents are herein incorporated by reference.        
Media signal sources generally support respective sets of encoding types allowing them to communicate with various other media signal sources. Specific examples of encoding types used to encode speech signals include ITU-T Recommendations G.729, G.726, G.723.1, G.722, G.722.1 and G.728 amongst others. Media signal sources are generally designed to be downward compatible and, as such, media signal sources implementing enhanced, and hence more complex, encoding functionality will usually also implement basic, and hence less complex, encoding functionality. Typically, in order to allow all the participants of a conference to communicate with one another, all the participants of the conference transmit media data packets to the conference bridge including media information encoded using an established common encoding type. This “common” encoding type is typically communicated to the media signal sources when the signal sources negotiate to be admitted to the conference. Therefore, the common encoding type is frequently the encoding type supported by the media signal source that provides the least complex encoding functionality in the conference.
A deficiency with current conference systems designed to reduce the occurrence of back-to-back (tandem) encode-decode operations is that they do not provide any suitable functionality for supporting multiple encoding types within a given conference. Take an example where there are 100 participants in a conference call associated with 100 respective media signal sources and where 99 media signal sources implement a basic encoding type and an enhanced encoding type and 1 media signal source implements the basic encoding type only. In this case, the common encoding type for the conference is set to the basic encoding type. Therefore, unless all media signal sources in the conference implement the enhanced encoding functionality, the enhanced encoding functionality provided by the media signal source is essentially rendered nearly useless by current conferencing systems.
Consequently, there is a need in the industry for providing a conference bridge media signal source and a conference system that at least in part alleviate the deficiencies associated with the prior art.